In many scientific and medical fields circumstances occur in which it is desired to sample data at random intervals so as to develop an overall statistical picture. Often, measurements which are periodic in nature are erroneously treated as random, resulting in gross distortions in the statistical analysis.
For example, one field in which random sampling has proved to be extremely useful is the field of psychology which deals with behavior analysis and modification. If observations of a subject's behavior are made at intervals which are random, after a sufficient number of samples, a true picture of the subject's behavior begins to emerge. However, if the measurements are periodic or partly so, rather than being truly random, great biases can result. Particularly important errors can be made when the observer erroneously thinks that the measurements are being made randomly and is unaware of their periodic or event contingent nature. For example, if a subject is observed at certain times each day, e.g. hourly on the hour, the observed behavior may well be more indicative of customary or habitual behavior at the beginning of appointments (which often begin hourly) rather than providing an indication of behavior in general. Even more seriously, the subject may learn to anticipate the observations, thereby giving biased data.
In order for sampling techniques to provide unbiased estimates, the samples must be taken at truly random intervals, and not at periodic intervals or at observer chosen intermittent intervals which the observer subjectively feels are random. This is because what the observer subjectively feels is random may in fact represent, unknown to the observer, a periodic factor relating to the observer's own behavior or state of awareness. Clearly this method of taking data would add unspecified biases and distortions to the data. An independent and objective means of generating random time intervals is needed.
A number of random and pseudo random devices have been proposed for this purpose in the prior art. One class of prior art devices uses an endless tape loop or program disc which has a fixed number of randomly spaced marks for triggering an alarm as they are moved past a sensor. Such devices are only pseudo random because eventually the pattern will repeat and the subject may become subconsciously aware of the pattern. Other prior art devices have used various types of electronic circuits with varying degrees of success at achieving a true random function. Some of such prior art devices are either too complex to be conveniently portable, or too costly for widespread applicability. In certain types of behavior analysis and modification described herein, a highly portable random interval generator which is so small and convenient that it does not interfere with ordinary activities is essential.
Behavior analysts have used prior art devices to cue sampling of an individual's behavior. For example, the time study engineer (either directly or photographically) may observe a machine operator and record by tallying appropriate categories whether the operator was engaged in one activity or another at the instant of the cue. After a sufficient number of samples, the proportion of time the operator spent engaged in each category of activity may be reliably estimated. While truly randomly spaced cues are preferable even in this procedure, one form of bias is eliminated since the operator does not know at what instant he was observed, so he can not learn to predict when the next intermittent sample will be taken.
In order for an observer to analyze the behavior of a subject over the wide ranging course of the subject's daily behavior (a distinctly different problem from observing a machine operator at his post), the apparatus for generating random intervals must be conveniently portable. A further requirement for long term in vivo monitoring is a method of recording the appropriate tallies which is portable and maximally convenient for the observer. Furthermore, it should be possible to record tallies only at appropriate times, that is, when the signal sounds, to prohibit accidental recording. These requirements are particularly important when the observer analyzes his own behavior so that the act of recording minimally alters his own environment and he is prevented from biasing the observations by recording tallies without his having received the signal.
A well-known principle of behavior modification is that, if a reinforcing event follows temporally an instance of a particular class of behaviors, the relative frequency of that behavioral class will increase. Furthermore, if a punishing event follows temporally an instance of a particular behavioral class, that class' relative frequency will decrease. A wide variety of events may serve as reinforcers if the subject is properly trained: examples are a particular sound, presentation of a light of a particular color, etc. Very often, one of the best reinforcers is objective numerical feedback of the number of prior successes. Analogously true is the variety of punishing events.
It is widely accepted that it is difficult for an individual to apply the rules of reinforcement and punishment to his own behavior, since their application requires the individual to withhold reinforcement from himself until his behavior meets a particular criterion. Randomly cued presentation of either a reinforcing or a punishing event, the choice between the two depending on the observed recent stream of events, obviates the aforementioned difficulty, and is conceptually markedly different from the prior art operant conditioning rules.